Humans have been using wood fires for heating somewhere between 400,000 and a million years. Today, though, using wood involves some compromises. Modern wood-burning systems have much, much lower emissions than old ones, but still can emit more than 100 times as much pollution as oil or gas furnaces, inside and outside your home. Some communities have even banned woodstoves for this reason.

But in other areas, wood is the preferred heating option because of price, lack of availability of other fuels, or simply some individuals’ economic or political commitment to live "off the grid," independent of utilities and energy companies. If a household has available timber, wood is virtually a free source of energy. Another plus for using wood is that it contributes less to global warming than burning fossil fuels. Oil, gas, coal, and wood all give off carbon dioxide as they burn. But if a tree is replanted for one that was cut down to use for fuel, it will absorb carbon dioxide as it grows, offsetting the emissions from burning. Of course a full environmental advantage only exists if the wood is harvested sustainably, without damage to the forest environment.

Here’s a guide to the various kinds of wood-heating units. Some use wood pellets instead of wood, obtaining higher efficiency with lower emissions.Top Tips

At home

* Make sure your stove is EPA-approved. Burning wood emits "microparticulates," the very fine particles in smoke and soot and can cause serious lung and circulatory problems. If wood is your heating choice, don’t burn it on an old stove (or an old-fashioned fireplace) that vents straight up the chimney. Purchase a new stove. Older stoves and fireplaces can emit from 8 to 30 times as much as soot as those built after EPA set new standards for emissions in 1988. If your stove meets the EPA standards, it will have a permanent "U.S. Environmental Protection Agency" tag including the date of manufacture on the back. Not only do the new stoves pollute far less, they are much more efficient, which will save you wood.

* Don’t let your air dry out. A heating stove in the house tends to dry out the air, which can irritate the nose and throat, aggravating sinusitis and other diseases. Ideally, indoor air should be around 45% humidity. To prevent dry air, place a kettle or pot of water on the stove or use a humidifier.

* Keep it clean. Wood stove outlets and chimneys need to be cleaned periodically. A heavy coating inside a chimney can actually set your house on fire. Have chimneys and equipment inspected by a chimney sweep or stove dealer if do not want to do the cleaning yourself.

When shopping, look for

* An Energy Star. The cleanest, most efficient woodstoves are EPA Energy Star-approved, and exceed the standards set by federal law.

* The right size. As with other types of heating systems, it's important to get a stove sized to meet your needs. The maximum heat output can range from 15,000 to 75,000 Btu per hour. When you visit a dealer, bring your home’s floor plan with dimensions, because this will help fit the stove to the design of the house.

o If you only plan use the stove to heat a single room or a small cottage, buy a smaller capacity stove. o Midsize stoves are usually adequate to heat smaller houses or cottages, especially if they are well-weatherized and insulated. o Large stoves are best for large houses with open floor plans (rather than separate rooms that can be closed off).

* Good stats. The stove’s label will also list its emissions, efficiency, and the amount of heat it’s capable of producing.

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Other Considerations

* There are two basic types of woodstoves, "catalytic" and "noncatalytic." The catalytic models have a "converter" inside that re-burns the gases and particles that would otherwise go up the chimney. This provides greater efficiency and steadier heat with lower emissions than most noncatalytic models. What’s not to like? Catalytic models generally cost more, and their converter requires more frequent cleaning, maintenance, and (every six years) replacement. The converter is also finicky—it can be damaged if foreign substances like plastic or other refuse are burned in the stove.

* If you like the environmental and cost advantages of woodstoves, but don’t want the inconvenience of cutting, or hauling, storing, or lugging wood inside, plus more frequent feeding of fuel, ash removal, and chimney cleaning, a wood pellet stove may be your best choice. It burns inch-long pellets made from wood wastes such as sawdust that might otherwise have been thrown away. Compared with wood stoves, pellet stoves

o generally burn cleaner and convert more of their energy into heat than wood stoves. Pellet stoves range from 75% to 90% efficient, compared with ordinary woodstoves, which run from 62% to 72%. Although a ton of pellets is only about a third the volume of a cord of wood, it can deliver just about as much heat. o cost more ($1,300 to $3,000, as compared with woodstoves, which generally range from $200 to $1,200) but are easier to maintain and do not require an insulated or masonry chimney system because less heat goes up the chimney. o are more complicated because they have thermostats and use an electric motor to feed the pellets into the stove from a hopper. The hopper requires filling far less often than a wood stove requires adding fuel.

* Although you may think of woodstoves in terms of old-fashioned self-reliance, their installation is not a job for every do-it-yourselfer. Wood fires are extremely hot—up to 2,000ºF, and therefore stoves must be placed on noncombustible material and either be set at the proper distance from anything combustible, or have the combustible areas protected by inflammable material. Pipes and chimneys should be properly installed in accordance local codes.

Benefits...

...to youA low-emission woodstove emits far less soot than other models, which means cleaner, healthier air in your home. It also requires a lot less lugging of wood and ash removal.

...to your walletIf you have a free supply of wood, a stove can cost less to operate than any other type of heating except passive solar. If you buy wood, an efficient stove will cost much less to operate than an inefficient one. The heat produced by different kinds of wood varies widely from 12 million to 33 million Btu per cord.

...to the EarthWood is a renewable resource, and using it means less dependence on climate-changing fossil fuels and often less environmental damage than is involved in the extraction, processing, transporting, and burning of fossil fuels. Modern stoves that meet or exceed EPA standards emit far less soot and other air pollutants than inefficient stoves and fireboxes (but still more than oil or gas heating systems).

Getting Started

* To find out if woodstoves might be problem where you live, contact your local air quality district. You can find it on the EPA’s website.

* Some utilities offer rebates to customers who buy energy-efficient woodstoves and pellet stoves. Check with your utility or search DSIRE, a national online database of incentives for energy-efficiency improvements and renewable-energy systems.

* If you decide to hire a professional to install your stove, here are some tips.

o Don’t use any company that tries to sell older equipment or seems to be dumping equipment by offering big discounts. o Ask for a bid in writing that specifies the equipment to be installed, the work to be done, and the total price, including labor costs. o Get more than one bid, and don’t jump at the lowest price. Better installers may charge more, but if they do a better job with a better system, you will save in the long run.